Patent Application
20080001125
Among the several advantages achieved by the present invention include stability of the inhibitor composition at high temperatures and, surprisingly, capability to achieve comparable or near-comparable corrosion inhibition, when a given total amount of the inventive inhibitor composition is compared with using, for example, a thiophosphorus compound or phosphate ester alone. This means that, by including only a minor proportion of the phosphorus-based compound along with a major proportion of a sulfur-based compound such as tropylene and/or a nitrogen-based compound, the problems associated with adding phosphorus, such as catalyst impairment, can be avoided or greatly mitigated, while still achieving excellent inhibition of naphthenic acid induced corrosion in hydrocarbon fluids, particularly at high temperatures. In other, non-limiting embodiments, either the sulfur-based compound or the nitrogen-based compound may be used alone or in combination with each other, without the use of any phosphorus-based compound.
The hydrocarbon fluids of particular interest in this invention are those fractions formed during crude oil refining processes. Such include, in one non-limiting embodiment, those that include, at least in part, gas oils and light lubricating oils. These hydrocarbon fluids are typically heated to a temperature in the range of from about 175° C. to about 400° C., and more particularly from about 205° C. to about 400° C. At these temperatures naphthenic acid induced corrosion, as well as corrosion attributable to other similar organic acids or phenols such as cresylic acid, particularly in these lighter fractions, is extremely aggressive and difficult to inhibit. The method and compositions of the present invention are particularly suited to such non-aqueous liquids and to protection of iron-containing metal surfaces.
In order to inhibit the corrosion is such hot hydrocarbon fluids, the compositions of the invention are typically added to the fluid. The fluid may be still cool or already heating or heated. In other non-limiting embodiments the stream may be previously treated or otherwise converted, and as such may form, for example, the feed to a distillation unit or reactor.
The inventive corrosion inhibitor compositions have, in one non-limiting embodiment, at least two distinct constituents. Of these, a major portion comprises at least one sulfur-based compound, or one nitrogen-based compound, or a combination thereof. As used herein, the term “major portion” is defined to mean more than about 50 percent and, in some non-limiting embodiments, it is at least about 60 percent; and in other non-limiting embodiments, it is at least about 75 percent; and in still other non-limiting embodiments, it is at least about 85 percent; by weight based on the total inhibitor composition.
The sulfur-based constituent is defined as comprising at least one compound conforming to one of the following formulas:
wherein R is independently —H, —SH, —SR, —SSR or C1-C12 normal or partially or fully branched alkyl that is saturated or unsaturated.
Some non-limiting examples of such sulfur-based compound include tropylene (1,2-dithiole-3-thione), which conforms to
1,2,4-dithiazole-3-thione, which conforms to
combinations thereof; and the like.
In some non-limiting embodiments the second constituent of the novel inhibitor compositions may be nitrogen-based. This constituent comprises a compound conforming to one of the following formulas:
wherein R is independently —H, —SH, —SR, —SSR, or C1-C12 normal or partially or fully branched alkyl that is saturated or unsaturated.
Non-limiting examples of nitrogen-based compounds include, in general, phenanthridines and acridines. Non-limiting examples of these include acridine, phenanthridine, octahydroacridine (OHA), octahydrophanthridine (OHP), 1,3-thiazole, combinations thereof, and the like.
In some non-limiting embodiments of the present invention, either the sulfur-based constituent, or the nitrogen-based constituent, or a combination thereof, may be employed as the sole or primary constituent of the corrosion inhibitor composition, i.e., this constituent is present in major portion. In other non-limiting embodiments, either of these categories of compounds may be included, alone or together, in a composition including a phosphorus-based constituent, provided that the nitrogen-based constituent is present, in total, in minor portion in the overall inhibitor composition.
As used herein, the term “minor portion” is defined to mean less than about 50 percent of the total inhibitor composition. In some non-limiting embodiments it is less than about 40 percent; in other non-limiting embodiments it is less than about 25 percent; and in still other non-limiting embodiments it is less than about 15 percent; by weight based on the total inhibitor composition. The phosphorus-based compound, or compounds, are selected from the group consisting of (a) thiophosphorus compounds of FORMULA 1 wherein R1 is R3(OCH2CH2)n or R3(OCH2CH2)nO; R2 is the same as R1 or XH, each X being independently sulfur or oxygen; provided however that at least one X is sulfur; R3 is an alkyl group of from about 6 to about 19 carbon atoms; and n is an integer of from about 0 to about 12; (b) salts of the thiophosphorus compounds; (c) alkyl and aryl esters of the thiophosphorus compounds; (d) isomers of the thiophosphorus compounds; and (e) phosphate esters. The inhibitor composition may include just one of the above phosphorus-based compounds, or any combination thereof, provided that, when included, the total of these compounds remains a minor portion, as that term is defined hereinabove, of the corrosion inhibitor composition as a whole.
For example, in certain non-limiting embodiments a selected thiophosphorus compound may be an alkyl dithiophosphonic acid of FORMULA 1 wherein R1 and R2 are each R3(OCH2CH2)nO, each X is sulfur, R3 is an alkyl group of about 8 to about 10 carbon atoms, and n is an integer from about 3 to about 5. In another non-limiting embodiment, two compounds may be selected, in one of which R1 is R3(OCH2CH2)nO, and in the other of which R1 is R3(OCH2CH2)n. In the present invention, wherever more than one component, e.g., one or more compound or combination of compounds, is selected, such may be added to the hydrocarbon feed or stream in separate doses or they may be combined into an additive composition prior to their addition. In still another non-limiting embodiment, a thiophosphorus compound may be included along with an isomer thereof and/or with a phosphate ester. In yet another non-limiting embodiment, R1 and R2 each correspond to R3(OCH2CH2)nO, and each X is sulfur, and R1 and R2 are the same, thus forming an alkyl dithiophosphoric acid as described in U.S. Pat. No. 3,909,447, which is incorporated herein by reference in its entirety. Preparation of alkyl dithiophosphoric acids is discussed in U.S. Pat. No. 3,909,447, and some are commercially available. Compositions of that patent may be effective in this invention, and the full scope of those compositions described as within the scope of the claims of that patent may be selected for use in the present invention. Such compositions often also comprise isomers of the thiophosphorus compounds as well.
Alternatively or additionally, the phosphorus-based compound may be a thiophosphinic acid. These compounds correspond to FORMULA 1 wherein each of R1 and R2 is R3(OCH2CH2)n, with R1 preferably but not necessarily being the same as R2, one X (most preferably the X double bonded to the phosphorus) is sulfur and the other X is sulfur or oxygen (most preferably, sulfur), R3 is an alkyl group of about 6 to about 18 carbon atoms and n is an integer from 0 to about 12. Preferred identities and ranges of the variables are as discussed hereinabove with respect to the alkyl dithiophosphoric acids. Thiophosphinic acids are known and certain forms are commercially available.
Yet another form of the thiophosphorus compounds is a thiophosphonic acid, corresponding to FORMULA 1 wherein R1 is R3(OCH2CH2)n, R2 is XH, one X (most preferably the X double bonded to the phosphorus) is sulfur and each other X is sulfur or oxygen (most preferably, sulfur), R3 is an alkyl group of about 6 to about 18 carbon atoms and n is an integer from 0 to about 12. Again, preferred identities and ranges of the variables are as discussed with respect to the alkyl dithiophosphoric acids.
The salts and alkyl and aryl esters of any of such thiophosphorus compounds may also be employed, either in combination with the acids or in place of them. Exemplary of types of suitable salts are discussed in U.S. Pat. No. 3,909,447, which is incorporated herein by reference in its entirety. Although they are discussed therein solely with respect to the alkyl dithiophosphoric acid, equivalent salts may be formed with the other thiophosphorus compounds. The esters may be formed by reaction of any of the noted thiophosphorus compounds with an alcohol. Preferred alcohols have up to about 18, preferably up to about 12, more carbon atoms. Thus, they are of the form R*OH, wherein R* is an alkyl or aryl group of up to about 18, preferably up to about 12, more carbon atoms than does the thiophosphorus compound from which they are derived.
The isomers of the thiophosphorus compounds are generally dimers. Often, as discussed in U.S. Pat. No. 3,909,447, they are formed inherently in the preparation of the thiophosphorus compounds. In a preferred embodiment, therefore, the corrosion inhibitor composition is a mixture of alkyl dithiophosphoric acid and isomers thereof in accordance with the teachings of U.S. Pat. No. 3,909,447, in addition to the sulfur-based constituent. However, as noted, the compositions of the invention need not include a mixture of the phosphorus-based compounds, but may include only one such compound, along with the sulfur-based and/or nitrogen-based constituent.
Generally, the isomers are of the formula
wherein X1 represents sulfur, X2 represents sulfur or oxygen, R1 is as defined in previous formulas, and R4 is the same as R1 or corresponds to the formula R3(OCH2CH2)ns, wherein R3 is as defined above. In some non-limiting embodiments, it is desirable that R4 is the same as R1 and X1 is sulfur. A mixture of isomers with alkyl dithiophosphoric acid, as described in U.S. Pat. No. 3,909,447, may also be selected for the phosphorus-based constituent.
Where a phosphate ester is chosen as all or part of a phosphorus-based constituent, in one non-limiting embodiment it conforms to the formula
wherein X is independently sulfur or oxygen, and R is independently —H, —SH, —SR, —SSR, or C1-12 normal or partially or fully branched alkyl that is saturated or unsaturated. Examples of the phosphate esters include, for example, phosphate ester itself, thiophosphate ester, ethoxylated thiophosphate ester, combinations thereof, and the like.
The most effective amount of the corrosion inhibitor composition of the present invention to be used in accordance with this invention may vary, depending upon the local operating conditions and the particular hydrocarbon being processed. Thus, the temperature and other characteristics of the acid corrosion system would typically be considered in determining the amount of inhibitor composition to be used. Variations in the ratios of the components within each constituent may be made and may, in some cases, produce preferred results under different conditions and in different corrosion systems.
In general, where the operating temperatures and/or the acid concentrations are higher, a proportionately higher amount of the corrosion inhibitor composition will be required. It has been found that the concentration of the corrosion inhibitor composition may range from about 10 ppm to about 5,000 ppm or higher. It has also been found that it is preferable to add the inhibitor composition at a relatively high initial dosage rate, in one non-limiting embodiment from about 2,000 ppm to about 5,000 ppm, and to maintain this level for a relatively short period of time until the presence of the inhibitor induces the build-up of a corrosion protective coating on the metal surfaces. Once the protective coating is established, the dosage rate needed to maintain the protection may in some non-limiting embodiments be reduced to an operational range. Such operational range may be from about 10 to about 100 ppm, desirably from about 10 to about 50 ppm, and more desirably from about 10 to about 25 ppm, without substantial sacrifice of protection.
While the gas oil and other crude oil fractions often contain naphthenic acid which contributes to the corrosion problem which is particularly addressed by the present invention, the inhibitor compositions of the invention are useful in not only that part of a refinery handling these petroleum intermediates, but are also useful throughout an oil refinery in which acidic hydrocarbons are in contact with iron-containing metal surfaces.
The description hereinabove is intended to be general and is not intended to be inclusive of all possible embodiments of the invention. Similarly, the examples hereinbelow are provided to be illustrative only and are not intended to define or limit the invention in any way. Those skilled in the art will be fully aware that other embodiments within the scope of the claims will be apparent, from consideration of the specification and/or practice of the invention as disclosed herein. Such other embodiments may include selections of specific sulfur-based, nitrogen-based, and phosphorus-based compounds, and combinations of such compounds; proportions of such compounds; mixing and usage conditions, vessels, and protocols; hydrocarbon fluids; performance in inhibiting or controlling corrosion; and the like; and those skilled in the art will recognize that such may be varied within the scope of the appended claims hereto.
A number of kettle tests were run. These tests were carried out in a resin vessel at a temperature of about 550° F. (−287° C.) in hydrocarbon fluids having acid numbers of about 4. The acid number was calculated based on the amount of a commercial grade of naphthenic acid with a nominal acid number. The vessel was heated with a heating mantle, which is controlled by a thermocouple and commercially-available temperature controller. Sparging with 1 percent hydrogen sulfide gas in argon introduced a constant level of sulfide. The sparge gas was first passed through a 100 mL graduated cylinder filled with water, and then through an empty 100 mL graduated cylinder. The second graduated cylinder was a trap to avoid backflow of hot liquids as the vessel cooled. Stirring at about 400 rpm with a paddle stirrer provided moderate agitation and velocity.
Corrosion rates were calculated based on the 20-hour weight loss of carbon steel coupons immersed in the hydrocarbon fluid. Results of the tests are shown in Table 1. In that table the “Inhibitor” column specifies whether no inhibitor was used (“Blank”); and where an inhibitor was used, whether it was: (1) a sulfur-based inhibitor as defined in the present invention, used alone (in this case, it is tropylene), denominated “Sulf-Inhib”; (2) a commercially-available phosphorus-based inhibitor, denominated as “Phos-Inhib” (not as defined in the present invention); (3) a thiophosphate inhibitor as defined in the present invention, denominated “TPE-Inhib”; or (4) a combination of the sulfur-based and thiophosphate inhibitors in the proportions shown, according to the present invention. “Weight” is shown in grams. “Mpy” refers to mils per year, which was the estimated annual weight loss based on the average loss resulting from each set of two coupons.
The test results showed that comparable or near-comparable inhibition was achieved by the inventive compositions in comparison with those including only the commercially-available phosphorus-based inhibitor.
Additional tests were run according to the method of Example 1 and at the same temperature (550° F., 287° C.). However, in this series of tests the amount of inhibition (“% Inhib.” and “Avg. % Inhib.”) occurring in each test was also calculated. Results are shown in Table 2.
Gas oil obtained from a refining company processing high acid crude oil, having a TAN of from about 4.5 to about 5.0, was kettle-tested according to the protocol of Example 1, except that the temperature was about 600° F. (−315° C.). Inhibitors were added to the gas oil in the amounts shown, and the mpy was averaged over 20 hours, with each value given representing three coupons tested. Results are shown in Table 3.
This application claims the benefit of U.S. Provisional Application No. 60/818,086, filed Jun. 30, 2006.
| Number | Date | Country | |
|---|---|---|---|
| 60818086 | Jun 2006 | US |
